86 research outputs found
Modeling the Jovian subnebula: II - Composition of regular satellites ices
We use the evolutionary turbulent model of Jupiter's subnebula described by
Alibert et al. (2005a) to constrain the composition of ices incorporated in its
regular icy satellites. We consider CO2, CO, CH4, N2, NH3, H2S, Ar, Kr, and Xe
as the major volatile species existing in the gas-phase of the solar nebula.
All these volatile species, except CO2 which crystallized as a pure condensate,
are assumed to be trapped by H2O to form hydrates or clathrate hydrates in the
solar nebula. Once condensed, these ices were incorporated into the growing
planetesimals produced in the feeding zone of proto-Jupiter. Some of these
solids then flowed from the solar nebula to the subnebula, and may have been
accreted by the forming Jovian regular satellites. We show that ices embedded
in solids entering at early epochs into the Jovian subdisk were all vaporized.
This leads us to consider two different scenarios of regular icy satellites
formation in order to estimate the composition of the ices they contain. In the
first scenario, icy satellites were accreted from planetesimals that have been
produced in Jupiter's feeding zone without further vaporization, whereas, in
the second scenario, icy satellites were accreted from planetesimals produced
in the Jovian subnebula. In this latter case, we study the evolution of carbon
and nitrogen gas-phase chemistries in the Jovian subnebula and we show that the
conversions of N2 to NH3, of CO to CO2, and of CO to CH4 were all inhibited in
the major part of the subdisk. Finally, we assess the mass abundances of the
major volatile species with respect to H2O in the interiors of the Jovian
regular icy satellites. Our results are then compatible with the detection of
CO2 on the surfaces of Callisto and Ganymede and with the presence of NH3
envisaged in subsurface oceans within Ganymede and Callisto.Comment: 9 pages, A&A, in pres
On the volatile enrichments and composition of Jupiter
Using the clathrate hydrates trapping theory, we discuss the enrichments in
volatiles in the atmosphere of Jupiter measured by the \textit{Galileo} probe
in the framework of new extended core-accretion planet formation models
including migration and disk evolution. We construct a self-consistent model in
which the volatile content of planetesimals accreted during the formation of
Jupiter is calculated from the thermodynamical evolution of the disk. Assuming
CO2:CO:CH4 = 30:10:1 (ratios compatible with ISM measurements), we show that we
can explain the enrichments in volatiles in a way compatible with the recent
constraints set from internal structure modeling on the total amount of heavy
elements present in the planet.Comment: Accepted in ApJLetter
On the composition of ices incorporated in Ceres
We use the clathrate hydrate trapping theory and gas drag formalism to calculate the composition of ices incorporated in the interior of Ceres. Utilizing a time-dependent solar nebula model, we show that icy solids can drift from beyond 5 au to the present location of the asteroid and be preserved from vaporization. We argue that volatiles were trapped in the outer solar nebula in the form of clathrate hydrates, hydrates and pure condensates prior to having been incorporated in icy solids and subsequently in Ceres. Under the assumption that most of volatiles were not vaporized during the accretion phase and the thermal evolution of Ceres, we determine the per mass abundances with respect to H2O of CO2, CO, CH4, N2, NH3, Ar, Xe and Kr in the interior of the asteroid. The Dawn space mission, scheduled to explore Ceres in August 2014, may have the capacity to test some predictions. We also show that an in situ measurement of the D/H ratio in H2O in Ceres could constrain the distance range in the solar nebula where its icy planetesimals were produce
Formation of Giant Planets- An Attempt in Matching Observational Constraints
We present models of giant planet formation, taking into account migration and disk viscous evolution. We show that migration can significantly reduce the formation timescale bringing it in good agreement with typical observed disk lifetimes. We then present a model that produces a planet whose current location, core mass and total mass are comparable with the one of Jupiter. For this model, we calculate the enrichments in volatiles and compare them with the one measured by the Galileo probe. We show that our models can reproduce both the measured atmosphere enrichments and the constraints derived by Guillot et al. (2004), if we assume the accretion of planetesimals with ices/rocks ratio equal to 4, and that a substantial amount of CO2 was present in vapor phase in the solar nebula, in agreement with ISM measurement
Determination of the minimum masses of heavy elements in the envelopes of Jupiter and Saturn
We calculate the minimum mass of heavy elements required in the envelopes of
Jupiter and Saturn to match the observed oversolar abundances of volatiles.
Because the clathration efficiency remains unknown in the solar nebula, we have
considered a set of sequences of ice formation in which the fraction of water
available for clathration is varied between 0 and 100 %. In all the cases
considered, we assume that the water abundance remains homogeneous whatever the
heliocentric distance in the nebula and directly derives from a gas phase of
solar composition. Planetesimals then form in the feeding zones of Jupiter and
Saturn from the agglomeration of clathrates and pure condensates in proportions
fixed by the clathration efficiency. A fraction of Kr and Xe may have been
sequestrated by the H3+ ion in the form of stable XeH3+ and KrH3+ complexes in
the solar nebula gas phase, thus implying the formation of at least partly Xe-
and Kr-impoverished planetesimals in the feeding zones of Jupiter and Saturn.
These planetesimals were subsequently accreted and vaporized into the hydrogen
envelopes of Jupiter and Saturn, thus engendering volatiles enrichments in
their atmospheres, with respect to hydrogen. Taking into account both
refractory and volatile components, and assuming plausible molecular mixing
ratios in the gas phase of the outer solar nebula, we show that it is possible
to match the observed enrichments in Jupiter and Saturn, whatever the
clathration efficiency. Our calculations predict that the O/H enrichment
decreases from 6.7 to 5.6 times solar (O/H) in the envelope of Jupiter and from
18.1 to 15.4 times solar (O/H) in the envelope of Saturn with the growing
clathration efficiency in the solar nebula.Comment: Accepted for publication in The Astrophysical Journa
Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan's atmosphere
We describe a scenario of Titan's formation matching the constraints imposed
by its current atmospheric composition. Assuming that the abundances of all
elements, including oxygen, are solar in the outer nebula, we show that the icy
planetesimals were agglomerated in the feeding zone of Saturn from a mixture of
clathrates with multiple guest species, so-called stochiometric hydrates such
as ammonia hydrate, and pure condensates. We also use a statistical
thermodynamic approach to constrain the composition of multiple guest
clathrates formed in the solar nebula. We then infer that krypton and xenon,
that are expected to condense in the 20-30 K temperature range in the solar
nebula, are trapped in clathrates at higher temperatures than 50 K. Once
formed, these ices either were accreted by Saturn or remained embedded in its
surrounding subnebula until they found their way into the regular satellites
growing around Saturn. In order to explain the carbon monoxide and primordial
argon deficiencies of Titan's atmosphere, we suggest that the satellite was
formed from icy planetesimals initially produced in the solar nebula and that
were partially devolatilized at a temperature not exceeding 50 K during their
migration within Saturn's subnebula. The observed deficiencies of Titan's
atmosphere in krypton and xenon could result from other processes that may have
occurred both prior or after the completion of Titan. Thus, krypton and xenon
may have been sequestrated in the form of XH3+ complexes in the solar nebula
gas phase, causing the formation of noble gas-poor planetesimals ultimately
accreted by Titan. Alternatively, krypton and xenon may have also been trapped
efficiently in clathrates located on the satellite's surface or in its
atmospheric haze.Comment: Accepted for publication in The Astrophysical Journa
New Jupiter and Saturn formation models meet observations
The wealth of observational data about Jupiter and Saturn provides strong
constraints to guide our understanding of the formation of giant planets. The
size of the core and the total amount of heavy elements in the envelope have
been derived from internal structure studies by Saumon & Guillot (2004). The
atmospheric abundance of some volatile elements has been measured {\it in situ}
by the {\it Galileo} probe (Mahaffy et al. 2000, Wong et al. 2004) or by remote
sensing (Briggs & Sackett 1989, Kerola et al. 1997). In this Letter, we show
that, by extending the standard core accretion formation scenario of giant
planets by Pollack et al. (1996) to include migration and protoplanetary disk
evolution, it is possible to account for all of these constraints in a
self-consistent manner.Comment: Accepted in APjL. 2 color figure
Constraints from deuterium on the formation of icy bodies in the Jovian system and beyond
We consider the role of deuterium as a potential marker of location and
ambient conditions during the formation of small bodies in our Solar system. We
concentrate in particular on the formation of the regular icy satellites of
Jupiter and the other giant planets, but include a discussion of the
implications for the Trojan asteroids and the irregular satellites. We examine
in detail the formation of regular planetary satellites within the paradigm of
a circum-Jovian subnebula. Particular attention is paid to the two extreme
potential subnebulae - "hot" and "cold". In particular, we show that, for the
case of the "hot" subnebula model, the D:H ratio in water ice measured from the
regular satellites would be expected to be near-Solar. In contrast, satellites
which formed in a "cold" subnebula would be expected to display a D:H ratio
that is distinctly over-Solar. We then compare the results obtained with the
enrichment regimes which could be expected for other families of icy small
bodies in the outer Solar system - the Trojan asteroids and the irregular
satellites. In doing so, we demonstrate how measurements by Laplace, the James
Webb Space Telescope, HERSCHEL and ALMA will play an important role in
determining the true formation locations and mechanisms of these objects.Comment: Accepted and shortly to appear in Planetary and Space Science; 11
pages with 5 figure
A primordial origin for the atmospheric methane of Saturn's moon Titan
The origin of Titan's atmospheric methane is a key issue for understanding
the origin of the Saturnian satellite system. It has been proposed that
serpentinization reactions in Titan's interior could lead to the formation of
the observed methane. Meanwhile, alternative scenarios suggest that methane was
incorporated in Titan's planetesimals before its formation. Here, we point out
that serpentinization reactions in Titan's interior are not able to reproduce
the deuterium over hydrogen (D/H) ratio observed at present in methane in its
atmosphere, and would require a maximum D/H ratio in Titan's water ice 30%
lower than the value likely acquired by the satellite during its formation,
based on Cassini observations at Enceladus. Alternatively, production of
methane in Titan's interior via radiolytic reactions with water can be
envisaged but the associated production rates remain uncertain. On the other
hand, a mechanism that easily explains the presence of large amounts of methane
trapped in Titan in a way consistent with its measured atmospheric D/H ratio is
its direct capture in the satellite's planetesimals at the time of their
formation in the solar nebula. In this case, the mass of methane trapped in
Titan's interior can be up to 1,300 times the current mass of atmospheric
methane.Comment: Accepted for publication in Icaru
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